How Far Should Your LED Be From Cannabis Plants?
Every LED is different, so a single number is useless on its own. What works is a starting height by stage, then adjusting based on what the top leaves tell you.
Starting heights by stage
Seedlings: 24-30 inches with the driver dimmed to 25-40%. Vegetative: 18-24 inches at 50-75%. Flower: 16-20 inches at full power. These are starting points for a typical 480W quantum board over a 4x4 area.
Reading the plant
Too close shows up as bleached white or pale yellow tips on the tallest colas, upward-taco leaf edges, and burnt tips while the rest of the plant looks fine. Too far shows as long internode spacing and thin, stretchy stems.
If only the tallest tops look stressed, that is a distance problem, not a nutrient problem. Raise the light two inches and wait three days.
Dimming beats raising
Raising a light spreads its footprint thin and wastes intensity at the edges. If your fixture has a dimmer, reduce power instead of raising the fixture whenever you can.
Frequently asked questions
- Can I use the back of my hand to check?
- It is a rough heat check only. LEDs run cool while still delivering intensity that bleaches leaves, so the hand test misses light burn entirely.